https://www.motorcyclespecs.co.za/model/kawasaki/kawasaki_klr650%2006.htmThe KLR650 motor is a 650cc, 100mm x 83mm, liquid cooled 5 speed unit.
These folks list the KLR "Max Power" at 48 @ 6500 RPM, RW HP at 41.7, about 6 HP drive train losses, fairly normal.
KLR all-up Wet Weight is listed at roughly 420, which seems low. The KLR weight is carried higher up than the BSA's weight will be as it is a dual purpose machine.
The BSA 650 specs by Rush Lane say 45HP @ 6000 RPM, wet weight of 213Kg/ 470 pounds. 45/48=about 94%, so within 6% of the KLR power spinning at 92% or the KLR's crankshaft speed.
As Derottone clearly pointed out, the stock exhaust is likely made of lead/depleted uranium just like all quiet modern systems, which this forums participants routinely replace anyway at the drop of a hat. It's not unusual to see a 20-30 pound savings with an exhaust swap out. Quite possibly the BSA would end up within 20 pounds of the KLR's weight, with a lower CG, and possibly a bit better midrange. The KLR's are routinely lowered anyway by folks that either spend more time on the street or have short inseams. The BSA offers more "traditional" styling than the clean-sheet KLR. The old Yamaha SRX6 was a nod in the BSA's (Clubman) direction, as were the GB 500 Hondas, but never had an "Old School" appearing, purpose built powerplant.
According to AutoCarIndia the BSA will retail for about the same as the W800 & Triumph Street Twin, so around $9000 USD (7,000 Pounds). That puts it $2500-$3500 more than the 650 Royal Enfield. I'm guessing that the retail will drop a bit after the "me first" crowd thins out.
https://www.rushlane.com/bsa-gold-star-650-specs-officially-revealed-12410304.html