I wear a pair of Gaerne G-Midland boots. I've done about 7,000 miles across SE Asia in them (off-road and Tarmac) and they have held up well. The left hand boot is no longer waterproof but I wear Sealskinz socks when it's raining anyway, no boot keeps out the monsoon rain for long. The sole on the G-Midlands is replaceable but both original soles are lasting very well and they offer decent grip when you find yourself pushing the bike through muddy lands slips. I probably don't need to tell you to avoid 'adventure' boots that have irreplaceable soles, not least if you drag feet when pulling away (I drag both when I exit petrol stations in Asia -to scrub off the inevitable sticky diesel that always surrounds the pumps) My boots don't have metal toe caps but are tough enough.
Gaerne don't import the G-Midland into the UK but shops in Europe have them on EBay, I chose this particular boot because of good reviews on adv forums and in yank magazines.
I go through a fair amount of gear which breaks or wears out, but these boots are up to the job.
Comfy too, once worn in.