normally aspirated twins would struggle to hold 4,000' AMSL on one engine, probably more like 3,500; which is less than the MSA over just the hills of the UK. Add turbocharging and you're probably well to the right of relatively 'affordable' compared to a decent high performance single, even then don't expect much above 8,000'.
Should read "most knackered old training type twins..."
I agree the BE76 or Seminole have pretty crap SE performance.
I'd rather fly a
decent twin any day though. With a SE if the engine fails you have one option, go down. Most light twins I've flown can fly quite happily on one engine, even when moderately loaded. Turbo's make a great difference though and even the likes of a Twin Star with 3 POB and overnight baggage and lots of fuel (probably at Max UUW) will happily climb on one engine to a good altitude.