I have a 310 125bhp Custom, It is well built but sluggish, when motorway driving you need to drop a gear when on an incline, A little research reveals the custom's gearing is to long hence poor acceleration, If you opt for the 330 model the gearing is lower to allow for the extra weight, giving better performance...I got my info from transit owners forum
My last van was a trafic 2.0 115, this was more car like to drive and a fair bit quicker than the custom
The custom goes back in July, I might replace with the 140bhp trafic or a custom 155bhp 330
If going for a custom i would advise opting for the stereo upgrade, load liner, heated front screen