I can vouch for XSLTel, he optimized my VPS (load was +3 and now its below 0.4). He did such a great work. I had myself installed eaccelerator, tuned the mysqld & httpd etc, but it didn't reduce the load. When I contacted XSLTel, he reduced the load to 0.3 at once. I was like WTF ? What magic did you do ?

He just said, he optimized the PHP Handler and optimized my MySQL engine

The optimization was epic and since then, my load is average 0.4, never gone above 0.6 (at peak times too).

Also, DLow, has done major server works in the past, you can go and check his thread about server management. I have hosted one of my sites on his server in the past and the server never gave any sort of problem.