i've used the 6500ks for veg with excellent results so i guess i am pretty loyal to them performing well. and yes, always pretty short compact internodes with t5s. plants generally have longer internodes when they are trying to get closer to their lightsource to get more light so perhaps under t5s the plants get enough light where they arent interested/concerned in getting closer as they are already perfectly content.
this is the bulb i use. idk much bout its spectrum but it appears a purplish color when on. emits UVB rays for reptiles and works great for plants too as far as increasing resin production.