Just under 1% slower than Arduino studio with this compile settings...

platformio.ini

@@ -1,40 +1,36 @@
-; PlatformIO Project Configuration File
+; PlatformIO Project Configuration File https://docs.platformio.org/page/projectconf.html
-;
-;   Build options: build flags, source filter
-;   Upload options: custom upload port, speed and extra flags
-;   Library options: dependencies, extra library storages
-;   Advanced options: extra scripting
-;
-; Please visit documentation for the other options and examples
-; https://docs.platformio.org/page/projectconf.html
 
 [env:genericSTM32F103C8]
 platform = ststm32
 board = genericSTM32F103C8
-; board = bluepill_f103c8
 board_build.mcu = stm32f103c8t6
 board_build.core = maple
 framework = arduino
-lib_ignore        = USBComposite/, FreeRTOS701, FreeRTOS821, FreeRTOS900, Ethernet_STM, libmaple
-
 lib_deps =
     greiman/SdFat @ ^2.0.4
 upload_protocol = stlink
+; Older gcc version produces much faster binaries than the latest.
 platform_packages = toolchain-gccarmnoneeabi@1.40804.0
 build_unflags = 
+    -Os
+    -DARDUINO_ARCH_STM32F1
 build_flags = 
-    -D PIO_FRAMEWORK_ARDUINO_STANDARD_LIB
-    -w
     -O3
-    -std=gnu11 -std=gnu++11 -nostdlib -mthumb -march=armv7-m -D__STM32F1__ -DARDUINO_ARCH_STM32 -MMD
+    -w
-    -ffunction-sections -fdata-sections
+    -DDEBUG_LEVEL=DEBUG_NONE
-    -funroll-loops
+    -DARDUINO_GENERIC_STM32F103C
-    -D DEBUG_LEVEL=DEBUG_NONE
+    -DARDUINO_LIB_DISCOVERY_PHASE
+    -DARDUINO=10813
+    -DARDUINO_ARCH_STM32
+    ; --param max-inline-insns-single=500 ; PlatformIO doesnt like this?
 
 ; Possible work around for clones, untested.
 ; https://community.platformio.org/t/cannot-upload-to-stm32-bluepill-board-over-stlink-v2/3492/25
 ; upload_flags = -c set CPUTAPID 0x2ba01477
 
+; Unsure if needed to ignore anymore or not.
+; lib_ignore = USBComposite/, FreeRTOS701, FreeRTOS821, FreeRTOS900, Ethernet_STM, libmaple
+
 ; [env:debug]
 ; build_type = debug
 ; debug_tool = stlink