All good - with two uglies!
The GIIB/III series of aircraft are quite simply the some of the hottest machines you will ever fly. Lets' start with the fact that the British put afterburning RR Speys on the F-4 Phantoms. That's your engine.
Its climb performance is nothing short of spectacular. Climbing at 300 KIAS above 10,000 MSL you lose steam at about FL260 but get it right back after the mach changeover. She climbs at .75M very nicely - I've seen sustained values over 3,000'/minute above FL370 at intermediate weights. Time to climb to FL410 at max gross is about 22-24 minutes depending on temperature. the GIIB is generally a littel more spry in the climb than the III - it's a little shorter and lighter with the same engines.
I am happier in a steam gauge, DC-powered IIB or III than in an EFIS, AC-powered III. As far as the electricity is concerned I think the DC airplane offers more electrical redundancy and therefore, more ways to solve electrical woes. The AC plane is nice - you can have the APU alternator in the air if you like and everything's automatic - but it's a better system altogether on the IV.
As far as the instruments go, the EFIS packages I've flown in the III are generally very early versions of EFIS and they're not very friendly, or very useful for that matter. A lot of the first generation stuff is just crap. It looks fancy but it's nothing special.
As for going across the pond, which one did you have in mind? I've been to Hawaii, Saipan, Macau, Hong Kong, Singapore, NewZealand, Australia, Russia, England, Ireland, France, Germany, Switzerland ... you get the idea.
Now for the downside. They DO burn a LOT of fuel. Idle is about 1000#/hour a side and takeoff flow can exceed 8000#/hour a side. It calms down once you get to altitude so it's a darn good thing it'll get you there straight out of the box. If you want range you'll need to slow to about .77M. if you want speed and don't care about the fuel bill you can go .84M if you like. I've flown our GIIB from Buenos Aires to San Juan, PR non-stop and I've flown our IIIs from Stanstead to Teterboro, also non-stop. It takes planning and a willingness to change plans on a moment's notice but it can be done.
The other problem IS indeed noise. These planes are about as loud as they come. The engines are basically the product of the Century Series fighter era. There are two new stage III hushkits available. I have experience with the QTA version. It's produced by the same guys that did the BAc-111s out there and it works pretty well.
Amazingly simple in the way it works the modification esssentially replaces the stage II exhaust cookie-cutter with a more up-to-date version and adds a ring shroud behind the cookie-cutter to shield some of the noise. Reverser movement is unchanged with VERY simple mechanical provisions made to get the shroud out of the way as a product of reverser deployment. That adds up to being a good thing because reverse is EXTREMEMLY effective on the GIII. It is not at all uncommon to be able to stay off the brakes until you're out of reverse - even on shorter runways!
I landed at Telluride the other day and exited WELL before the end of the runway. Didn't touch the brakes until I started to cancel reverse at 70 knots. When I got out and checked the temperature of the rims I could lay my hand flat on them indefinitely without flinching.
Finally, the STC adds a new bullet to the front of the engine. It's a longer, sleeker bullet with sound absorption properties. The addition of the bullet to the package not only got the noise down outside the plane but also produced a 20% reduction in interior noise as well. A GIII with this STC is just about as quiet as a G-IV inside. I know this from experience having flown an unmodified GIII, a modified GIIB, and a G-IV all in the same day.
To put all this in a nutshell, i have a friend who recently went to go work for brand X. He was given a Challenger to manage and I asked him once how he liked it. His response was, "Well, it ain't a Gulfstream." Nothing else really needs to be said.
The GIII is arguably the 727 of the corporate world. Aged? Perhaps but venerable anyway. Noisy? You bet! But that noise will get you a long ways from the ground VERY quickly! If you can get a chance to fly one of these planes I'd say DO IT!
TIS