Ive had those same problems then i got powerstrip (
http://www.entechtaiwan.com/ps.htm) and it solved everything. It oc's yur video card and do a bunch of stuff with it and makes SH run 30% better. Just install and rite click the system tray icon and goto performance profiles and then configure and move yur clock speeds up by 5 on both (have to stay together) until yur screen starts to act wierd, then go back a few until all is good. Then SH fps will run about 20 frames faster in all areas. Dont worry about wrecking yur card or anything. Its completely safe. Just read all the info on it if yur afraid. But ive used it forever.