I don't think the estimation from the server will be perfect to give you exactly the right number of getworks. It will only ever be approximate within a range of timeframes. If you run cgminer 2.7.6 it will show you what diff shares you are submitting now.
I upgraded cgminer from 2.7.5 to 2.7.6 today and ran it for a few hours on both a regular server, and the dynamic test server to compare them.
This is with a regular server (us3.eclipsemc.com:8337):
cgminer version 2.7.6 - Started: [2012-09-25 13:50:55]
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(5s):1878.9 (avg):1596.6 Mh/s | Q:154 A:1979 R:6 HW:0 E:1285% U:15.9/m
TQ: 0 ST: 3 SS: 0 DW: 17 NB: 14 LW: 5007 GF: 1 RF: 0 WU: 22.1
Connected to http://us3.eclipsemc.com:8337 with LP as user ---
Block: 00000343360189b2e6653ae3f7eb361e... Started: [15:28:23]
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[P]ool management [S]ettings [D]isplay options [Q]uit
BFL 0: 59.8C | 803.7/798.9Mh/s | A:1000 R:4 HW:0 U: 8.06/m
BFL 1: 62.7C | 803.8/797.7Mh/s | A: 981 R:2 HW:0 U: 7.90/m
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[2012-09-25 15:52:31] Accepted 0e608cb9 Diff 1 BFL 0 pool 0
[2012-09-25 15:52:33] Accepted 55ff4821 Diff 1 BFL 1 pool 0
[2012-09-25 15:52:42] Accepted 05ec9fc0 Diff 1 BFL 0 pool 0
[2012-09-25 15:52:42] Accepted b1fc8319 Diff 1 BFL 0 pool 0
[2012-09-25 15:52:47] Accepted 0276cffd Diff 1 BFL 0 pool 0
[2012-09-25 15:52:48] Accepted 2753bbc0 Diff 1 BFL 0 pool 0
[2012-09-25 15:52:55] Accepted 5110c078 Diff 1 BFL 1 pool 0
[2012-09-25 15:52:55] Accepted d42a26ae Diff 1 BFL 1 pool 0
[2012-09-25 15:53:00] Accepted b950b119 Diff 1 BFL 1 pool 0
[2012-09-25 15:53:05] Accepted 55edde49 Diff 1 BFL 1 pool 0
[2012-09-25 15:53:09] Accepted 00e85f88 Diff 1 BFL 0 pool 0
[2012-09-25 15:53:09] Accepted 8cfcad21 Diff 1 BFL 0 pool 0
[2012-09-25 15:53:14] Accepted 71bc86cd Diff 1 BFL 0 pool 0
[2012-09-25 15:53:21] Accepted 9d78a652 Diff 1 BFL 1 pool 0
[2012-09-25 15:53:25] Accepted c50b2095 Diff 1 BFL 0 pool 0
[2012-09-25 15:53:30] Accepted 217974b9 Diff 1 BFL 0 pool 0
[2012-09-25 15:53:41] Accepted 9a920baf Diff 1 BFL 0 pool 0
[2012-09-25 15:53:41] Accepted 7ed0bb23 Diff 1 BFL 0 pool 0
[2012-09-25 15:53:43] Accepted 2a6c466f Diff 1 BFL 1 pool 0
[2012-09-25 15:53:46] Accepted 9857a9d5 Diff 1 BFL 0 pool 0
[2012-09-25 15:53:48] Accepted b5c1cc2e Diff 1 BFL 1 pool 0
[2012-09-25 15:53:52] Accepted 6743b6ff Diff 1 BFL 0 pool 0
[2012-09-25 15:53:52] Accepted 2dc972cb Diff 1 BFL 0 pool 0
[2012-09-25 15:53:54] Accepted 77e4d753 Diff 1 BFL 1 pool 0
[2012-09-25 15:53:59] Accepted 29a11631 Diff 1 BFL 1 pool 0
[2012-09-25 15:54:02] Accepted 6571c1ed Diff 1 BFL 0 pool 0
[2012-09-25 15:54:18] Accepted bab78252 Diff 1 BFL 0 pool 0
[2012-09-25 15:54:20] Accepted 02da1ab3 Diff 1 BFL 1 pool 0
[2012-09-25 15:54:27] Accepted 4d5210ee Diff 1 BFL 1 pool 0
[2012-09-25 15:54:29] Accepted 99466391 Diff 1 BFL 0 pool 0
[2012-09-25 15:54:31] Accepted 7ea77f2b Diff 1 BFL 1 pool 0
[2012-09-25 15:54:31] Accepted 636bd8f8 Diff 1 BFL 1 pool 0
[2012-09-25 15:54:47] Accepted 8e54c592 Diff 1 BFL 1 pool 0
[2012-09-25 15:54:50] Accepted 8cba9563 Diff 1 BFL 0 pool 0
[2012-09-25 15:54:58] Accepted b2b6e95e Diff 1 BFL 1 pool 0
[2012-09-25 15:55:01] Accepted 66a19fcb Diff 1 BFL 0 pool 0
[2012-09-25 15:55:01] Accepted 1bebd1a8 Diff 1 BFL 0 pool 0
This is with the dynamic test server (us3.eclipsemc.com:8437):
cgminer version 2.7.6 - Started: [2012-09-25 15:56:27]
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(5s):1468.6 (avg):1582.5 Mh/s | Q:238 A:1003 R:0 HW:0 E:421% U:8.3/m
TQ: 0 ST: 3 SS: 0 DW: 50 NB: 15 LW: 4656 GF: 1 RF: 0 WU: 22.1
Connected to http://us3.eclipsemc.com:8437 with LP as user ---
Block: 00000005f1bf5387d0157105a798cd0e... Started: [17:56:50]
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[P]ool management [S]ettings [D]isplay options [Q]uit
BFL 0: 59.8C | 677.6/791.6Mh/s | A:508 R:0 HW:0 U: 4.20/m
BFL 1: 62.6C | 675.1/791.6Mh/s | A:496 R:0 HW:0 U: 4.10/m
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[2012-09-25 17:53:19] Accepted 49cb55c7 Diff 3 BFL 0 pool 0
[2012-09-25 17:53:41] Accepted 02086e52 Diff 3 BFL 0 pool 0
[2012-09-25 17:53:57] Accepted 2e7f4139 Diff 3 BFL 0 pool 0
[2012-09-25 17:54:02] Accepted 0075386a Diff 3 BFL 1 pool 0
[2012-09-25 17:54:02] Accepted 1a00b705 Diff 3 BFL 1 pool 0
[2012-09-25 17:54:02] Accepted 4a2ed23d Diff 3 BFL 1 pool 0
[2012-09-25 17:54:07] Accepted 4557f784 Diff 3 BFL 0 pool 0
[2012-09-25 17:54:18] Accepted 3655886d Diff 3 BFL 1 pool 0
[2012-09-25 17:54:23] Accepted 4441bebe Diff 3 BFL 1 pool 0
[2012-09-25 17:54:29] Accepted 3b213e0d Diff 3 BFL 0 pool 0
[2012-09-25 17:54:29] Accepted 1605cab9 Diff 3 BFL 0 pool 0
[2012-09-25 17:54:50] Accepted 47808422 Diff 3 BFL 0 pool 0
[2012-09-25 17:54:56] Accepted 13c76db5 Diff 3 BFL 0 pool 0
[2012-09-25 17:54:56] Accepted 2542d6cc Diff 3 BFL 0 pool 0
[2012-09-25 17:55:01] Accepted 0321f232 Diff 3 BFL 1 pool 0
[2012-09-25 17:55:01] Accepted 39169afd Diff 3 BFL 0 pool 0
[2012-09-25 17:55:11] Accepted 49a31924 Diff 3 BFL 1 pool 0
[2012-09-25 17:55:12] Accepted 0da5cfc7 Diff 3 BFL 0 pool 0
[2012-09-25 17:55:17] Accepted 262aabc0 Diff 3 BFL 0 pool 0
[2012-09-25 17:55:17] Accepted 1732aeab Diff 3 BFL 0 pool 0
[2012-09-25 17:55:28] Accepted 26c27c9f Diff 3 BFL 0 pool 0
[2012-09-25 17:55:33] Accepted 1fb350f5 Diff 3 BFL 1 pool 0
[2012-09-25 17:55:33] Accepted 385fe40c Diff 3 BFL 0 pool 0
[2012-09-25 17:55:38] Accepted 196fe903 Diff 3 BFL 1 pool 0
[2012-09-25 17:55:44] Accepted 4cc5006d Diff 3 BFL 0 pool 0
[2012-09-25 17:55:54] Accepted 25339073 Diff 3 BFL 1 pool 0
[2012-09-25 17:55:59] Accepted 276ed065 Diff 3 BFL 1 pool 0
[2012-09-25 17:56:00] Accepted 184a84f4 Diff 3 BFL 0 pool 0
[2012-09-25 17:56:00] Accepted 05b945fc Diff 3 BFL 0 pool 0
[2012-09-25 17:56:10] Accepted 19dcec1f Diff 3 BFL 1 pool 0
[2012-09-25 17:56:32] Accepted 41e5c544 Diff 4 BFL 0 pool 0
[2012-09-25 17:56:42] Accepted 3e5718c1 Diff 4 BFL 0 pool 0
[2012-09-25 17:56:50] LONGPOLL from pool 0 detected new block
[2012-09-25 17:57:05] LONGPOLL from pool 0 requested work restart
[2012-09-25 17:57:16] Accepted 062c4e21 Diff 4 BFL 0 pool 0
[2012-09-25 17:57:16] Accepted 14c46c49 Diff 4 BFL 1 pool 0
[2012-09-25 17:57:22] Accepted 04c7a1ba Diff 4 BFL 0 pool 0