"911"s (not racing variants) weren't even very good cars until they came out with the 993 C4,
Or more so when they came out with the 986 (Boxster) where they put the engine where it should be. This is why, whilst running almost the same engine, the 911 is always tuned with a higher output. Embarrassingly for Porsche, when they did their testing at Nurburgring the Boxster was only 2 seconds slower than the entry level 911 Carrera, which came with almost twice the price tag. Something to be said for putting the engine in middle, just like the little X. The X1/9 was revered for it's handling but always lamented for it's lack of power.
Most comparisons are generally between the X1/9 and the TR7 for obvious reasons, but were usually between the earlier X1/9's, as that was the era (TR7 74 - 81) , and you're comparing a 2ltr engine vs a 1300, and even the later was only a 1500. The 2ltr TR7 would do 9.9s in the 0-60 and the 1300 X is 12.2s only improving to 11.2 in carb form, but still a sedately 12.2 in injection.
But as opposed to the 912E, a fairer comparison would be between the 914 as that has a more similar layout. I can't actually find any direct head to head comparisons due to a couple of issues, production overlap, with the 914 being from 69 to 76 and the X1/9 being 72 to 89, and the other being market, the Porsche being the upper end and the X being budget end. There are many head-2-heads with more like cars such as TR7's, MR2's and even Pontiacs Fiero, and earlier model comparisons to Spitfires, MG's, and again the TR7.
When you look at the stats, the 914 is equally anemic in 0-60 13.3s for the early 1700's, 12.0s for the 1800's, and was really only the 1900 flat 6 carburetored model that did 8.7s with a top speed of 129, vs the 115 for the X1/9 carburetored model.
Based on that, a 1500 X1/9 would hold it's own with all but the flat 6, as well as handling better and having that wonderful Bertone styling. The 914 wasn't exactly a pretty car, or overly good, which is probably reflected in its relatively short lived life of 7 years, especially when you consider the Boxster has already gone past 20 years.
As for the 912E, it was really the poor mans 911, and actually succeeded by the 914. ** (correction. The 912E was a 1 year wonder in 1976 only for the US market when the 914 ceased production, so ironically, the 914 succeeded the 912, only for the 912E to succeed the 914, to then be dropped for Porsche's foray into front engine cars, the 924, 944 and 928 with the 924 becoming the entry level Porsche)
