Hi guys, I have had some experience with the uk and Irish suppliers over the last few months so thought I would add my 2 bob.
Burton: have not had any major issues with them, have purchased from them twice. They always respond to my emails within a couple of days, whether that be for general sales enquiries or checking the status of my order. One of my small orders for a 30 pound crank bolt did not make it to me a couple of months ago and burton was happy to file their own insurance claim and resend the item after the 4 week insurance wait. One minor issue I did have was ordering a clutch part off their website which said the item was in stock, but turns out it wasn't and had to be manufactured by AP, so what should have been a few days wait turned into 5 weeks. Burton were sorry about it and kept me up to date with how the order was going. It is probably worthwhile to ask first before ordering as to stock availability, then follow them up on status order after you order. I think it was me who asked where the clutch part was when it didn't come after a few days only to find out it want actually in stock. Overall though the gentleman I have dealth with there, Ian has been good to deal with.
Raceline: have ordered a set of ITBs from them once. Not very responsive with general tech email questions, there have been a couple of queries I had that went unanswered over email. Might be best to call for tech questions. They were fine to deal with otherwise when ordering and their shipping was fast.
Grp4: really good to deal with, prompt over email and helpful with tech questions. Torsten was pretty patient with my multiple questions before I finally committed to an order, which was just a couple of weeks ago actually. Shipping was fast and production time estimates accurate. Recommended.
Pace Products: initially good to deal with though not super prompt, email response time was about 1 week. I was more disappointed with their 'custom' products and technical explanations. Bought a dry sump pump kit from them, specifically designed for a duratec. Whilst the pump and pump bracket are nice gear, the belt that came with it was way too big for the kit e.g. no tension. When I asked them to send me the right belt, they said that I should space out the bracket with washers to tension the belt - not good enough for a $1k purpose built kit and I had specifically asked them about belt tension before I ordered the kit!
TTV: good to deal with and very responsonsive to email queries. Ordered a flywheel from them, but the one they sent had the wrong crank bolt size. They were good enough to credit me a small amount to get the holes redrilled. Not ideal but at least post sales service was good.
Motorsport tools: good to deal with and very responsive to email queries. Had an issue with the brake kit I bought from them in terms of the correct bolt type v strut but they were happy to offer post sales advice.
Cheers.