There will be a difference if you change HS's but i doubt its worth the added cost, surely the XP-90 is no better than the SP-120 and the Ultra-120 or even the TT-BT but the temp drop could possibly be a little. maybe 2c ?
Your temps aren't that high, I don't think it's worth the 30-40$ unless you got money to burn. I just installed my XP-90 last week, had it sitting around as I could hit 2.6ghz on stock cooling. With summer and my move to a place that boils when i'm not home/ac not on I put the XP-90 on and temps dropped like 5C on average, not bad but amd64's are pretty cool chips to begin with.