This is something we've been made aware of and we suspect it is due to some major changes we made to our rendering engine to add support for streaming. We've got a task to birng our performance in-line with pre v2.5.0 but I couldn't say for sure when this will be available. I may be able to help you achieve some performance improvments though.
If you add the following class extension to SChartSeries
@interface SChartSeries ()
@property (nonatomic, retain) NSNumber *maxNumberOfPointsInBin;
You should then be able to set this
maxNumberOfPointsInBin property to a number that is larger than the total number of datapoints in your series. This should help offset some of the overhead created by our binning work, but I suspect that it won't bring you fully in-line with your pre-2.5.0 performance levels.
Other than above, you could reduce the number of datapoints rendered onto your chart at once, and be smart about how you provide data to your datasource. Loading in new data as your chart pans towards unpopulated parts of your chart could be one option, but this may require quite a bit of work on your part to get working smoothly!
I'll make sure we post back here as soon as we have any further information.