From 2002, basic pay at Royal Mail was increased so that you were no longer a “postman given an allowance on top to drive a HGV”.
When the basic increased however, the OVERTIME rates were crushed in an overall move that had already begun by 2002.
NDA was scrapped - paying time and a third on hours between 7pm and 6am.
Double Time at Weekends was replaced with either “single time” if you were on duty, or “standard overtime rate” if on overtime. You got a bit extra pensionable on sundays but that was about it, and you were expected to work bank holidays as “duty” rather than as 2.5x overtime.
Standard Overtime for a while was preserved at 1.65x rate, but this melted into 1.15x rate where it stands now.
The years-old tradition of “RM pay for your breaks” was also scrapped, and you now get deducted as much as 90 minutes a day off your gross hours at work for “meal breaks”. The 90 minutes kicks in at shifts 12 hours and above.
The optimum shift pattern to work at RM therefore becomes 4 x 10hr 55min shifts (43hr40m total) which will be reduced by 4x1hrs for meal breaks, meaning you’ll get paid 40:40 for the week. £407.50 if on £10ph at the agency for instance. This isn’t as bad as it looks for a 4 day week and all. Night Shift allowance as a full timer only pays out in full if the shift works across 10pm-2am, thus if you start at 22:10 hours or finish at 01:50hrs you’ll only get “late late” shift rate which is barely half the full night rate. When duties are re-written and a “re-sign” takes place, there is often a move by the firm to construct more duties who’s start/finish times are on the wrong side of these cut-offs. 
Basics at other firms are higher, but involve you working a longer basic working week that this - not that this is right and proper - so in the great scheme of things, IF you can get a nice shift, RM still pays a competitive wage for the time being. You can’t rely on overtime any more that’s all, but I did along with many others, and couldn’t easily swallow my pay dropping by £500pm plus in the last year before I left, because of the overtime cull.
As for the suggestion that RM drivers race about… I’d say no more than at any other firm. The “Job and Knock” element isn’t what it used to be on the basis of the duties having the guts cut out of them a long time since. My own opinion is that an incoming agency driver underestimates the ability of some of RM’s old bangers to go like the clappers when you put your foot down. Couple that, with agency folk on “content” runs being given the same amount of time as a full timer to do it - ie working to the 318. If you can do the job better than a full timer in other words, you might finish ahead, and still be paid for the 318 listed time for the duty - a latter day “Job and Knock” definition if ever there was one. 
Overall: 10hr55min shifts at RM are best. Flat 9 hours or 12+ hr ones are not so good, because of the disproportionately high amount of Meal Relief that is docked from it.
(Work 9 hours, get paid 8 - deduction about 11% work 12 hours, get paid 10.5 - deduction 12.5%)