As a shooting proposition, most people on here I think would plump for the Mk1 Premier, which probably has the nicest trigger, others for the Hurricane with its click-adjustable sights.
In terms of power, the little smoothbore Junior struggles to make 1.5 ft-lbs.
Mk1s and Premiers are more like 2-3.
Seniors, Hurricanes and Tempests according to official Webley velocity figures are around 3.5 ft-lbs, but the last two can be tuned to 4 or a bit more - export Tempests sent to the US for sale by Beeman often ran hotter than standard, having a more powerful spring.
I think the Turkish Tempests were also made with a more powerful spring (but they are generally not as nice as Birmingham ones).
Honestly (and I like Webley pistols and have four of them), if you want a classic spring pistol that shoots decent scores on a 10M target, there are better choices (eg the Diana model 5). If you want oomph, with a fair degree of accuracy, the BSA Scorpion or HW45 do that better.