Yes standard 50kg rail shoud be fine continuously welded for even 160kmh with TPWS and adequate lx protection. Trouble is these days teh standard available rail weights available in Australia are either 50kg or 60kg. So VLP for some strange reason wants 53kg which has to specially rolled. Probably because its the closest to the old 107lb rail. Another reason the rail operators should not be dictating the track standards, which should be the task of DOT. Rail operators should be just that running the railway with the key focuses being 1. that there is a train provided when it is scheduled 2. that such train runs to OT within the defined criteria at least 95 % of occasions.
I'm a little surprised 53kg is still available; it became redundant when 50 and 60 kg rail became available (circa 1980?). Soon after, 53kg was only available to special order in small quantities for maintenance replacements. I'm guessing 53kg availability is consumer lead.
As for 47kg (94lb), that's a really redundant rail. We should have jumped straight from 80lb (in it's many variants) to 107lb (53kg). It was perpetuated by the Commonwealth when the Commonwealth Railways (post WW2) adopted it as their standard rail, (that is why it went into the Nth East Std Gauge; It was even at that stage being considered as a secondary rail by certain sectors of the industry, but the Feds weren't going to pay any more, and VIC wasn't going to put their hand in their pocket for any reason.
So 50kg for secondary track and 60kg for mainlines. If a bigger rail is a bridge too far for the budget, increase capacity by closing up the sleeper spacing to say, 580mm.