moving on from BDP-S300
I've had my Sony BDP-S300 for a fair number of years now and I'm getting pretty sick of waiting a couple of minutes for it to switch on, then another 5 to load a blu ray.
It seems the more recently-released players load significantly quicker. Would there be a big difference in the peformance of the newer players in the £100-£200 area? If the newer Sony or Panasonic players are much better and load quicker I might be tempted to part with some cash!
You will definataly notice a huge difference. I have a Panasonic DMP-BDT210 which is a great bluray player IMHO, and is well within your £200 budget. I can't say i have timed it, but it goes from off to ready to play a lot quicker than the popcorn takes in the microwave (2 minutes). And if you've got a decent telly, you will probably see an improvement in the picture and motion handling too 
I was looking at the Panasonic actually. seems like a good player!
Yes, you will notice a significant improvement in loading times with curent players, especially Sony & Panasonic at your budget.
My Home Cinema Pioneer KRP 500A, Yamaha RX-V1900, MA Radius R225HD LCR, R90HD rears, AW12 sub, Panasonic BD60, PS3, Boxee Box, Sky HD, Boxee Box, Logitech Harmony One, Logitech PS3 Adapter, Sonos ZP90
Bedroom Samsung UE32C6510, PS3 slim white, Apple TV, Sonos S5, Sonos ZP90, Audioengine 2, Oppo OPDV971H
Miscellaneous: Synology DS212J + 2 X WD Red 2TB drives, WD 1TB NAS, Sonos ZoneBridge, BT HH3 as modem & AirPort Extreme router