You might as well go for the HO if it's an La7, cause he's just gonna do the same to you and then run like h*ll...
But seriously, if your "only" doing 250 knots, you'll need some speed to work with no matter what you do.
My first (and only) suggestion would be what I'd do wether I was at 250 knots or up to fighting speed:
Attempt to get some separation just prior to the merge, typically by beginning a zero G dive at max con distance. If the opposing pilot follows suit by diving with you then he's got game and your probably going to die anyway. If he stays level or dives to meet you with an HO at the last minute, you've a fighting chance
If the bandit flies level (lucky you), however unlikely that would be, begin pulling your nose up to meet the nme at the merge with your plane in the vertical (see, your already gaining turn degrees on him). At this point, no matter what he does, you already have up to half a circle of advantage on him and he is most definately in a defensive posture (or AFK, in which case you kill the dweeb, thanks the AH gods, and move on). This move is frequently known as a Vertical Lead Turn.
If he dives to meet you in an HO at the last minute (a more likely scenario), barrel roll to avoid the HO shot and continue your loop (that you started at the merge when you pulled the stick back to go vertical) as best you can so your upside down and looking below you to acquire a visual of the bad guy (he dove to meet you, remember). Now there's 3 things the bandit will likely do after his merge:
Dive away to extend and either setup for another HO pass or run home to his mommy. If he runs, flip him a 1 finger salute and climb for some alt to use on the next guy. If he comes back for the HO just keep trying to Lead Turn him (and attempt to get some seraration prior to the merge) and hope he gets frustrated enough to fight - if all he knows is the HO then at least the fight will be something close to an even match. OK that's 2 things...
The 3rd thing he might do is pull his nose up to try and turn to meet you. This is good. He will likely be fast from his dive (if he dove from a very slow speed he will be able to turn into you better, in which case YOU should extend and re-acquire) when he tries to pull out of the dive he will be blacking out and burning his E in a very high G maneuver. he also will not be able turn very tightly, while you on the other hand will be above him and be able to simply (we hope) drop in on his tail with a substantial advantage in angles and begin the process of saddling up on him, or at worst getting into a rolling scissors where HE will be ahead of you and faster. Bad for him. ADVANTAGE MUCKMAW...
Now all of this is assuming your in similar performing aircraft. The nuances of the many types of matchups possible in AH are almost infinite. but with this one move you can often get off 1 good shot even when your Jug vs Spit. Obviously some gunnery skills and a little luck help out here.
Now go out there and do as I say, not as I do

Magoo