I'm not entering the fray as to who is or was or will be the best, but does anyone know whether there was any restructuring of the track distances between then and now? Certainly, as was touched on, but not developed, steeplechase jumps tended to be a couple of inches higher than they are now, and many have been re-positioned or done away with since, in the interest of track remeasuring or safety. If your horse of 30+ years ago was consistently having to clear jumps higher than now, there is an additional expenditure of energy involved (of course), which ought to be figured in to comparing your timings. Also, many courses since ARKLE's day have dropped - in the same races - a water jump, or taken out an especially tricky fence. You'd have to be sure that any comparisons were made on entirely equal race lengths (don't forget that nowadays many races don't state, as they used to, a flat 2m, but "2 miles about one furlong"); on equal numbers of jumps per race (ensure none were taken out since ARKLE lepped over them); on equal heights of jumps, and equal numbers of types of jumps - for example, was an open ditch taken out and replaced by an upright, or vice versa, or was a different run of jumps presented then as against now?
Also bear in mind that the going was tested with a walking stick in the 'old days', whereas now there is much more precise moisture measurement via the going stick, which provides a running reading around the course, resulting in Good, Good to Firm in Places; Soft, Heavy in Places, and so on, whereas in ARKLE's day, a few kicks of the heel, a few stabs with the old walking stick, and it was declared Good, or Firm, all over.
I might also chuck in weather conditions on the day - we've all noticed the extreme winds recently, I'm sure. At Brighton's last meeting, horses battled against a very brisk but warm wind to the start, had a cross-wind turning in, and a helluva tailwind spritzing them up the hill to the line. If ARKLE ran with any adverse wind conditions and those you wish to compare him to didn't, you really ought to consider him slowing down against cross or headwinds.
I'm not being obstructive here, but if you're going to read the entrails, you have to read them all.
It would be the same for comparing past and present athletes - not the least innovation, beyond completely different training methods, diet, spas, supplements, sports psychologists, personal Reiki masters and masseurs, etc., is the humble shoe. Jesse Owens ran like the wind in what schoolchildren did school sports in - a flat-soled Plimsoll. No anti-concussion sole, no orthotic insoles, no customised fit. Just banged them on and that was it. So, consider how he might've performed given today's non-smoking, diet-controlled, psyched-up, kitted and fitted environment. How often do you think he had his blood checked, his platelets counted, his respiration and heart rate monitored? It's just the same with good racehorses today - they're monitored for undue weight loss or gain, their feed's supplemented with vitamins and minerals, they're swimming, under heat lamps, given Shiatsu, Reiki and other complementary therapies (I'm waiting to hear that DENMAN has his own psychologist any day now), whereas I daresay ARKLE and other old-time top cohorts just got bunged out in a field on their rest days, instead of a salt bath and mood music.