Worth the upgrade?

I have been fiddling with my 25 Streamline. Currently set to shoot jsb kings at 875ftps for a fantastic 65 shots (huma regulator installed). I keep reading about slugs and shooting the heavies at 900ftps and I am wondering whether the Crown or Impact would be a worthy upgrade to get the heavies up to speed and try some slugs. Changing fac rated airguns in the UK is a faff so need to get any upgrade right (I only have a single slot for a 25 airgu) I tend to hunt in windy conditions to no more than around 70 to 80 yards and so far the Kings at 875ftps seem to be doing fine for me which leaves me swithering on an upgrade. We all like new toys but what really am I missing out on stuck with kings at 875: are the heavies at these speeds that much better? 
 
Easy answer. No. Heavies at 900 or even 950 are no better than at 875 FPS. If you decide to shoot slugs that's a whole new ballgame, but you can't shoot them from an ST barrel like your Streamline has anyway... So if you want to shoot slugs, the SL isn't your gun. However, at "no more than 70 to 80 yards", there is no advantage to slugs anyway... ;) And the Impact or Crown is certainly no more accurate with the Heavies than your SL...
 
I followed a thread from Chuck around 8 months ago that inspired the installation of the huma. He had also increased the pressure to 300 bar using new gauges etc... so sticking to 230 bar methinks shooting heavies at 875ftps for 60 shots is beyond my streamline. I am generally happy with my set up shooting the jsb kings but reading about slugs I can't help but feel I am missing out. Been offered a second hand crown or impact so pondering the upgrade although may not be worth it,