Andres, let me say right up front that I'm not an "experienced" Speedster owner. I've only ever had my P.O.S., so my frame of reference is limited to what my mechanic friend has imparted to me or what I've seen with my jalopy.
My old 1641 VeeDub engine probably wasn't taken care of properly before I got it, either. That didn't help. Then I drove it hard like it owed me money.
That said, assuming you take better care of your toys than I do, I'd still try to stay significantly south of 5K rpm with anything other than a race-prepped engine. I don't have any experience at all with VS, but my engine got really, really hot if I went faster than 70 and revved more than 4,500 rpm.
I'm defining really hot as more than two-thirds of the way up the meter; roughly 220 degrees after twenty minutes on the Interstate at 4K, in fourth, at 70 or so mph on a 65-degree day.
That transmission was a later-period, bone stock four-speed, and it wasn't really capable of sustaining even that. I pushed it too hard and wound up having to scrap both the engine and tranny after two years.
Jim Sartwell, who's putting my new running gear together, says I can go to about 6,500 rpm with the new 2366 engine and a 3:88 fourth. He advises shifting at 5,200 under race driving conditions, and significantly lower than that (3-4K) for normal driving. He expects to see a top speed of about 110-120 mph, but he wants to test that under safe conditions and measure his findings.
He has also insisted on a rev limiter to prevent running it up past 6,200 rpm, even though he provided a 10K tach as my only dash-mounted instrumentation.
The new engine was a drag engine until now, but the gear selections are all chosen from specific years of stock, split-case VW trannies.
As far as safety goes, I think that's relative to a lot of variables. Last year, my car would have been snapped off the chassis like a dandelion head off the stem if I had been hit broadside by anything. VS almost certainly has to be better-built than my car was. I'm paranoid, so I now have a cage and a helmet.