That was actually RCKen who pointed that out. His point was that many digital servos can use more power than standard servos of the same basic size & performance. This could result in using up your receiver battery quicker with the digitals than you would with the standards. The DX-7 comes with a good 1100mAh receiver battery though (at least mine did) so that should more than make up for the difference. The Spektrum receivers are very voltage sensitive so be sure to never fly if you even question the condition of the battery.

My advice on the DX-7 was based on the fact that all of the programming options can be a little overwhelming to someone brand new to flying. I do get your point of making the investment now though. If you go with it, just resist the urge to play with all the bells and whistles on your first plane. You won't need any of them for a basic 4-channel trainer.

Supporting your LHS is a great idea too. I'm surprised that they carry the Hobbico Avistar but not OS engines. Personally, I've seen a lot more trouble with new Evolutions than I have with OS. Still, they run great so long as you get a good one and it is tuned correctly. Like RCKen says, the .40 will be plenty of power in your trainer.