Yes,..you can be competative with a non-digital (analog servo) in a plane under 27% in size. As already stated,..thats all we had to fly with not to long ago.
Digitals are the way to go, especially if you are wanting to work on 3-D stuff (rolling harriers, walls, blenders, waterfalls,etc). My 40% Carden Cap had all analog Futaba (non-digital) servos in it. The areas you will loose performance as I noticed several years ago, was in the 3-D area especially. You have to have the holding power of the digitals, my Cap would perform well, but the servos (analog) gave up on me a bit more than I was comfortable with executing low level 3-D stuff.
Precission flying,......the digitals are critical by todays standards for leveling the playing field with your fellow competitors. Example:My last major IMAC type contest in 2003,..again I was flying the CAP 232 and we had to fly in a 25+ mile per hour cross wind and still execute at a high level. I was the only guy still flying analog servos (non-digital) I had flown my known round(Unlimited) and all the way through the flight I kept saying to myself,...something is wrong with this plane(232 was a borrowed plane, my 39% 330 primary plane was lost several weeks prior to the contest,..all digitals),..it's not flying right? The short story,...the servos were being worked to the max in the wind (stalling the servo) and by the the sequence and giving up (analog servos make max. torque at 60 degree's of deflection, digitals make it instantly for the sake of comparisson) and we don't fly with that much throw for precission stuff. My 15 flights of practice on the plane were in light winds,..had no idea!!! I even stripped out a pair of giant 3801's on the rudder executing a snap in the wicked wind,..nylon gears(older popular equipment set-up from past years,..outdated itself).
The investment,..material and time we put into our planes,...you really do not want to skimp on servos in regards to analog-vs-digitals. like most everyone in the post has said,...analog will work fine. Keep it in the smaller stuff,....no point by todays standards to use them in anything bigger. If your expectation is max preformance,..digitals all the way. If you just want to fly around and thats all some guys want to do,...analogs are fine,.use 130+ ounce minimum (JR make s a nice servos ST-126 I think??,..162 ounces on 6.0 volts and I can buy them at the hobby shop for about $33 bucks.
Best of Luck,
Advantage Hobby Fliton Field Rep/Custom Airframes of America/Dragon Fire Customs/Desert Aircraft/Carden Aircraft/JTEC Radiowave/Guardian America. NSRCA, Dist2 FAI/F3A/IMAC Unlimited,.not active.
Ed Alt,...the dual reg's work AWESOME!,...Thank you!