You answered your own question with your last statement, "you have so many more options with speed and alt".
The quick summary for 109G10 vs La7:
1) Don't let him (La7) get you low and slow, break off the fight at an alt where you know you can still use your speed to get away (~5K with WEP). I usually set my "combat floor" to something a couple of K above this so I can always dive to my best speed. Even if he's closing on you at 5mph you can usually force a long drag till help can arrive. The La7 guns are only effective out to about D350 with a steady target. A friendly with a target in tow usually attracts more friendlies to help. Ensure if you need to run, run to friendlies, not to the enemy side.
2) Don't pack gondolas. I never bring them in a G10 unless I'm specifically bomber hunting. In other 109's I do, but not the G10. It's performance is already bad enough that gondolas turn it into a dumptruck with guns. They also kill your top speed I think by as much as 25mph.
3) BnZ.. it's your best attack. The La7 really isn't much of a turner, but the G10 is far less so (especially at low speeds). If he starts to constantly turn then you have successfully set him up for BnZ or for someone else who's a better turner to pick off. Watch your speed carefully, the 109G10 can get away from you with too much speed in the blink of an eye. Don't dive from too high above in order to start your BnZ if it puts you into compression. Get to a comfortable alt above the target and then start your attacks.
4) Exploit the La7 between 9K and 16K altitudes where it has no performance gains (it actually gets slower and loses any WEP advantages in that range). The La7 at 9K will do basically ~400mph, at 16K is doing more like 380. The G10 on the other hand at 9K is capable of 405mph increasing to 420 at 16K (with WEP). Even more shocking is your climb rate at 10K (4500/min in G10 compared to only 2750 in La7) which gets even more lopsided at 16K
5) if you end up low and slow it means you are in a world of hurt unless friendlies can bail you out of trouble. If not, hope your chute was packed properly back at the airfield.
Hope this helps.
-Soda