It's kinda hard to figure out the point of the question and the question can't be answered until we know where you want to go. You hint at vertical performance, but there's so many factors....

Many modern airplanes, like 747's, are flying at T/W ratios as low as .25 and lower. Actually you can go lower, it's only a question of takeoff roll and drag. It also depends greatly on wing loading and total surface area (wetted area = prime source of drag). Of course a higher T/W is better, except that leads to other considerations like costs, structures, flutter, fuel load, etc.

I did a 14' wingspan twin ducted fan flying wing at 50 lbs. The measured installed thrust, using a lab force guage, flat out was 13lbs, both engines together. Nothing like the expected 20 lbs you would guess from all the hype. So we flew at .25 T/W. T/O roll was 300' and in flight speed at 100 mph+.

T/W isn't the only measure of performance or airworthiness. 12 bs of thrust can fly a 30 lb airplane if you want, it might even have great vertical performance if you get a good entry speed and have a low drag planform. Best though if you stick to the smaller sized jet kits.