Here's where we found the polars and/or data that can be made into polars:

http://www.willswing.com/Articles/Article.asp?reqArticleName=PolarData

175 fpm at 24 mph and 530 fpm at 47 mph, 6% increase in V2 for comp harness (which would give us 49.82 mph).

Converted: Minimum sink speed is 38.6 km/h, minimum sink rate is 0.9 m/s,  80.2 km/h at 2.7 m/s

Wills Wing's comment re streamlined harnesses indicates that a streamlined competition harness gives you a reduction in sink rate of 90 fpm at 50 mph.

http://www.aeros.com.ua/structure/support/polar_en.php

Combat L 13, all-up pilot weight – 87 kg, harness – Aeros Viper S, temperature at the ground – 12o C, VG on, maximal glide ratio – 16,7, minimal sink rate – 0.8 m/s (at 45 km/h). (2. 5 m/s at 80 km/h - taken from the accompanying graph.)

Converted:  Minimum sink speed 28 mph with minimum sink rate 157.5 fpm, at 49.7 mph, sink is 492 fpm.

http://moyes.com.au/productdetail.asp?id=115&pg=38&cat=

Minimum Sink Point: -0.9m/s 40km/h, High Speed Point: -2.5m/s 80km/h

Converted: Minimum sink speed is 25 mph with minimum sink rate 177 fpm, 492 fpm sink at 49.7 mph. Moyes indicates that streamlined harnesses are worth 40 fpm at high speeds.

What I take away from these values is that Moyes and Aeros claim the same sink rate at 50 mph, at almost 500 fpm, with Wills Wing claiming 530 fpm. Moyes and Wills Wing claim the same minimum sink rate at 175 fpm at 24-25 fpm, while Aeros claims 20 fpm less at 28 mph. The polar performance curves at minimum sink speed are pretty flat so the minimum sink speed could be any where between 23 mph and 28 mph.

Other than what Aeros tells us, we don't know the wing loading, or pilot hook in weight. Wills Wing doesn't differentiate between the 144 and the 154 models. We don't know at what altitude these polar values are for.

Taking these published values and creating polars basically by eye and by using manual curve fitting in FlyChart I produce a comparison polar chart:

It is very hard to say whether the values provided by the manufacturers are comparable. For example, why exactly would the Aeros Combat 13 L have a minimum sink rate 20 fpm less than the Moyes RS 4 or the Wills Wing T2? That makes a huge difference in the polars. If the minimum sink rate for the Combat L 13 is the same as the other two gliders than the polars would essentially be the same (at least we wouldn't have enough confidence in their measurement to be able to differentiate them).

Chris Arai states here:

Table 3 shows the glide polars in parabolic form used to make this analysis. Figure 4 shows the polars graphically. These polars are representative of modern gliders, however not very accurately. By that I mean that the accuracy of the measurement techniques used is not good enough to distinguish between different makes of high performance gliders. They are accurate enough for S2F, and have been used for a long time in the Tangent with good results.

Individual polars can be found here: Aeros, Moyes, Wills Wing.