RE: Simple Things to Add Speed - Your Tips
1) Keep them light. If there's any weight to be lost, put your planes on a diet. Heavy airplanes need more lift to stay in the air. More lift means increased induced drag and a slower aircraft. Like others above have noted, I have personally witnessed (upon multiple occasions) OS .32 dusts with small servos outrunning the same airframe with a larger engine and standard servos. I believe this is because of the weight / induced drag difference.
2) Make them slippery. Add fillets around the wings, cowl the engine, hide control linkages inside the wing/fuselage/tail. This can be done on smaller airplanes than you think. And for heaven's sake don't hang aileron servos under the wing or tail servos on the outside of the fuselage.
3) Don't use fixed gear if you can possibly get around it. Use retracts or learn to hand launch.
4) Use the right propeller. Short diameter and high pitch is the recipe for a high revving engine on a slippery model, and keep in mind that just because one engine seems to run well with a particular prop doesn't mean that it is the best match for every airframe. I like APC, others like wood props. Don't be afraid of over-square props, ie 8x9, 9x10... You may need to play with modifying props to suit your needs. I found that an APC 9x8 cut down to 7.5x8 worked very well on my last OS .32/Diamond Dust combo. I liked it better than the 8x8 cut down too. It always seemed as though the extra prop chord hooked up better on launch than the 8x8.
Suggestions for a simple speed plane:
-Q500 with any good .46-50. For more fun, cut the wing down to around 40" span and lose the gear.
-Diamond Dust/ Screamin Deamon/ Outlaw with a .32. My favorite .30-.35 engine was the OS .32SX. Sadly, they have been discontinued for about a year and a half but you may be able to find one on ebay every now and then.