Can I expect big OC improvements by removing the GPU shim and lapping the heatsink ?

Can anyone post results before and after ?

Thanx in advance

Specs:
AMD XP 2800+ (211x11.5) w/ CoolerMaster Aero 7+
Asus A7N8X Deluxe Rev. 2 (1007 bios)
Corsair TwinX 400mhz, PC3200LL (2 x 512) (6,3,2,2)
WD Raptor HardDrive (10,000 rpm, 8mb cache, ATA150)
ATI Radeon 9800 Pro w/ Thermaltake Giant 2
SB Audigy 2
Lite-on 16x DVD
Creative 52x Remote CDROM
Sony 52x/24x/52x Burner
Zalman ZM-RS6F Theater 6 Headphones
Altec Lansing ACS56 4.1 Speakers
PowerTek 500 watt PS (dual fans & gold plated)
Aspire X-Alien Black Case w/ 6 LED case fans

No.

Assuming you mean "big OC improvements" by lowered temps by doing both of those, then

Removing the GPU shim - no change in temps.

Lapping the heatsink - Maybe 1 or 2 degrees if it's bad.

1 or 2 degrees - maybe 1MHz difference if you're lucky. But if you're running at such high speeds that the temperature is the limiting factor...well...:rolleyes:

IMHO, CPU's are semi-OK to overclock, but video cards is a completely different story. I saw major problems with my first overclocking experiment on my Radeon 8500LE.

you left out what you're running it at now, what the highest you can go before seeing artifacts is, and what you're goal is. also what the temps are at now if you can get a reading of that.
Are you just going to lap the stock heatsink or were you thinking of slapping a new heatsink on there too? I see you already have the giant 2, so i don't think in this case you'll get a huge boost over your current setup, you should notice a slight boost though at least. if you're confident in the procedure go for it i guess, but that's a nice vid card to be playing with...
here's a good guide i came across, for a 9700, but same idea: http://sid.nrgservers.net/9700mod/

I've heard that by removing the R9700 shim many have had good results and better overclocks, but the shim on the R9800 is shorter, and the gpu core makes good contact w/ the heatsink/fan unit. Might get a little better by lapping, but best bet would be to add a cooling solution better than the stock one...